Le Van Banh - Hoang Bac Quoc

Transcription

1 Omonrice 11: (03) STUDYING AND FABRICATING SIMPLE SMALL DRYERS APPLIED IN SMALL FARMS ABSTRACT Le Van Banh - Hoang Bac Quoc The Agricultural Engineering Division (AED) of Cuu Long Delta Rice Research Institute (CLRRI) has studied, improved, and fabricated some prototypes of simple small dryer suitable to small farms located in remote areas. During 00 02, three dryer prototypes which have perfectly fabricated are: (1) Tent house using fans combine, (2) Standing cylinder dryer, and (3) Lying drum dryer. These dryers prototypes are well adapted to rice production at small holder level, especially in Cantho province. Their specifications included small dryer (drying capacity from 1.0 to 2.0 tons/batch), simple structure, easy fabrication, low investment, low drying cost, easy operation, short drying time and good grain quality (low broken rice percentage). INTRODUCTION Preharvest environment and postharvest handling influence grain quality. Rice breeding program has only concentrated varietal improvement on productivity, whereas all efforts of agricultural engineering has been paid attention to postharvest technology to enhance grain quality, mostly milling quality properties. Major grain quality problems can be listed as yellow and broken grain, risks in aging and storage, variety mixing and mislabeling, no discriminating different grain sizes for commercial request. Specific grain properties relevant in drying include moisture content (both critical and equilibrium moisture content), and hull or husk tightness. Delayed drying may result in sackburning of wet grain due to nonenzymic browning and microbial growth and mycotoxin production (in maize and parboiled rice). Improper and over drying may reduce head rice yield and aroma. In the Mekong delta of Vietnam, drying of high moisture content paddy harvested in the rainy season has become a major need to reduce yield loss due to postharvest and to increase rice quality. Issues in grain drying have been discussed at harvesting time. Constraints could be identified as (1) lack of compatible technologies including hardware; (2) lack of understanding of the mechanical drying process in both design and operation; and (3) lack of extension activities. In the other hands, we have to pay more attention to the current situation of small holders in which rice field varies from 0.5 to 1.0 hectare per farm, and almost farmers are poor so that they have not enough money to invest modern mechanical dryers. To meet the demand of these small-holders on post-harvest of rice production, studies on paddy dryers focussed some key features as low capacity (one to two tons per batch), simple structure, easy fabrication, low cost investment, low energy consumption, short drying time and good quality of drying product. Thus, the three dryers as (1) tent house using fans combine, (2) standing cylinder dryer, and (3) lying drum dryer, have been set up to meet the demand of these small holders. MATERIALS AND METHODS A. Tested dryer: The Agricultural Engineering Division of CLRRI studied and fabricated three small dryer models are: (i) tent house and blower combine type; (ii) standing drum type; (iii) lying drum type, and natural sunshine drying as control treatment. Three dryer prototypes were improved with drying bin structure recalculated blower (airflow m 3 /s, static airpress mmh 2 O column); recalculated furnace (heat supply for airdrying). B. Measuring items - Efficiency: time study and moisture content;

2 Studying and fabricating simple small dryers... - Uniformity: moisture content (every one hour); - Air temperature and humidity; - Grain temperature; - Grain quality: broken rice percentage C. Measuring methods Fuel and energy consumption: - Start full fuel tank and end of drying full tank measure quantity of fuel (diesel fuel); - Counting numbers of honeycomb coals, one unit weight of 2kg; Grain weight: - Initial weight and final weight must be measure by balance; Grain moisture content: - At the beginning everyone hour and later every two hours; - Sampling: Tent house at samples and samples; Lying drum at samples; Standing drum at samples; and sunshine drying at 5 samples. 7 Air temperature: continuously measured by thermos recorder: - Ambient air: temperature and humidity; - Heated air: temperature and humidity was controlled at 1 point / each dryer; - Grain temperature was controlled at sites for tent house; 2 sites for Lying drum; 2 sites for Standing drum; 2 sites for sunshine drying; - Grain quality: counting broken rice among 0 pieces / each dryer over 48 hours after drying. To compare rice-milling quality of dried paddy from dryer, pick up some paddy sample to dry in the sunshine (in shade). At last, to mill dried paddy samples and compare broken rice percentage among the treatments to control TESTING RESULTS 1. Structure of simple small dryers. A. Drying rice below tent house using fans combine improved Drying bin Burn Blower Fig.1. Schematic drawing of tent house using fans combine improved dryer-type (non express tent house part at here)

3 8 Le Van Banh et al. Paddy bed (a) stopper Paddy layer o o Plenum 30 o (b) Paddy layer 30 0 Fig. 2. Front Elevation of Paddy Bed of Tent house Drying (a): Roof shape none stopper; (b): Roof shape with stopper Fig. 3. Pictures of Tent house drying are operating

4 Studying and fabricating simple small dryers... 9 B. Lying drum dryer Position of Blower Inlet-outlet Burner Drying bin Frame Fig. 4: Schematic drawing of Lying drum dryer (Non express mobile frame part with wheels at here) Fig. 4: Lying Drum Dryer for Testing C. Standing cylinder dryer Plenum hamber Drying bin Fig. 5: Schematic drawing of Standing Dryer Frame Note: Exhaust air Burner Blower Outlet

5 130 Le Van Banh et al. (a) Drying Bin Frame (b) Operating Dryer Fig. 6. Pictures of Standing Cylinder Dryer 3. Testing, demonstration and transferring to farmers 3.1 Results of Drying Test on June, 13/6/02 Table 1. Outline of Drying Performance of 3 Dryer types (Variety OM25) Parameters Unit Dryer Type Note Tent house with fan combination dryer Standing cylinder dryer Initial rice weight kg 1, Initial Moisture content % Final Moisture content % Final Dry rice weight kg 1, Drying time h Drying rate %/h Drying capacity kg/h Consumption of fuel liters Consumption of coal unit Consumption of coal kg Drying cost of fuel VND 36, ,000.0 Drying cost of coal VND 58, ,000.0 Total cost (drying rice base) VND/Ton 60, ,5.0 Total cost (15% rice base) VND/Ton 51, ,969.0 Percentage of broken rice % Heated air temperature 0 C at outlet of oven Heated air humidity %RH at outlet of oven Drying air temperature 0 C in drying bin

6 Studying and fabricating simple small dryers... Omonrice 11: (03) 131 Table 1 indicates that 1. Tent house prototype shows drying time of 9.2 hours per batch and drying rate of 0.80%/h. Percentage of broken rice is 2.0%, and shows no problem. 2. Standing cylinder type has drying rate of 1.23%/h. The percentage of broken rice is 2.5%. 3. Drying rate of natural sunshine becomes very high, and the percentage of broken rice also expresses very high value of %. This event could be explained as i) It was sunny and windy, ii) Dried rice layer was 4-5cm thin, and iii) Temperature in rice got over 45 0 C (very high). But the meteorological value of that day is not clear, and it is necessary to check the air temperature, air humidity and wind velocity. (Table 1) 4. Mixing of 5 hours later after starting conducted high drying rate and the reduction of moisture deviation as shown in Fig The deviation of moisture content has two kinds. One is between the surface points and the bottom points, and the other is between the front points and the back points. When mixing, it is important to understand this matter. 6. The trend of the reduction of standing drum type and sunshine drying is shown in Fig.9 and Fig.10 Moisture Content (%w.b.) 26 Average Max Min Mixing drying time (hour) Fig.7 Drying Curve of Tent House Type Moisture Content (%w. M ixing Surface Bottom Moisture Content (%w. M ixing Front Back D rying Tim e (hour) D rying Tim e (hour) Fig.8. Difference of Drying Curve of Tent House Type among Sampling Points (13 June 02)

7 132 Le Van Banh et al. Moisture Content (%w.b.) Drying Time (hour) Fig.9 Drying Curve of Standing Type Dryer (13 June 02) Moisture Content (%w. 26 M ixing Surface Bottom Average Drying Tim e (hour) Fig.10 Drying Curve of Standing type Dryer (13 June 02)

8 Studying and fabricating simple small dryers Results of Drying Test on 19 June 02 Table 2: Outline of Drying Performance of tested 3 types (Variety OM90) Parameters Unit Tent house with fan combination dryer Dryer Type Standing cylinder dryer Sunshine Initial rice weight kg 2, , ,4 Initial Moisture content % Final Moisture content % Final Dry rice weight kg 1, , Drying time h Drying rate %/h 0, Drying capacity kg/h Drying capacity (15% rice) kg/h Consumption of fuel liters Consumption of coal unit kg/unit Consumption of coal kg Drying cost of fuel VND 40, ,300.0 Drying cost of coal VND 94, ,042.0 Total cost (drying rice base) VND/T 86, ,097.0 Total cost (15% rice base) VND/T 73, ,533.0 Percentage of broken rice % Heated air temperature 0 C at outlet of oven Heated air Humidity %RH ,9 at outlet of oven Drying air temperature 0 C in drying bin Environmental temperature 0 C Environmental humidity %RH Note Table 2 indicates that (1) Drying rate of tent house type is lower than that on 13 June as shown in Table 2. The reason is that (i) In the latter half of drying period, the burner of honeycomb coal had bad condition, and (ii) Sudden and strong rain fell at about 6 PM, and conducted high air relative humidity. The mixing method is recommended as shown in Fig.11, for reduction of two kinds of moisture deviation. The ratio of broken rice is small of 3.5%. (2) Lying drum type has good drying performance of drying rate 1.31%/h. The ratio of broken rice is small of 2.0% Moisture Content (%w.b M ax M in Average M ixing M ixing D rying Tim e (hours) Fig.11 Drying Curve of Tent House Type Dryer

9 134 Omonrice 11: Le Van Banh (03) et al. (3) In the test of tent house type, the mixing process has two times. The first mixing indicates that the drying rate increases so much, and the moisture deviation becomes so small. But the effect of the second mixing is not clear. (Fig.) So, it take need only one mixing has an enough effect in the case of this moisture content. Moisture Content (%w.b.) Front Drum 26 Back Drum Drying Time (hour) Moisture Content (%w.b.) Mixin Drying Time (hour) Position 1 Position 2 Position 3 Position 4 Average Fig. Drying Curve on Some Sampling Points of Lying Type Dryer Moisture Content (%w.b.) /0 6 Average Max Min / Drying Time ( hour) 21/0 6 Fig 13: Drying Curve of sunshine drying during June, 02

10 Studying and fabricating simple small dryers Running cost Table 3: Outline of Drying Performance of tested 3 type Date of Tested 02/6/13 02/6/19 02/6/ Rice variety OM25 OM90 OMCS00 Type of Dryer Tent Standing Sunshine Tent Lying Sunshine Tent Lying Initial rice weight kg 1, , , , Final dry rice weight kg 1, , , , Initial moisture % content Final moisture % content Removed moisture kg Drying time h Drying rate %/h Drying capacity kg/h Drying capacity kg/g (15% rice) Consumption of fuel liters Consumption of coal unit 29.0, Drying cost of fuel VND 36,000 30,000-40,800 36,300-27,000 9,000 Drying cost of coal VND 58,000 29,000-94,000 84,000-42,000,800 Total cost (dry rice VND 60,960 79,773-86,777 97,063-51,841 80,625 base) /T Total cost (15% rice VND 51,8 67,802-73,759 82,504-44,063 80,453 base) /T Cost of removing VND moisture 01kg Percentage broken % rice Ambient air 0 C temperature Ambient air humidity %RH Heated air 0 C temperature Heated air humidity %RH Rice temperature during drying 0 C Cost of Removing 1kg Moisture (VND) /06/02 19/06/ Type of Dryer Fig.: Running Total Cost of Removing 1kg Moisture of Tested Dryer 1: Tent House 1 13/06/02-2: Standing 13/06/02 4: Tent House 2 19/06/02-5: Lying 19/06/02

11 136 Omonrice 11: Le Van Banh (03) et al. Table 3 indicates that: (1) Capacity of tent house type is higher than that of the others, and so the total running cost is lower (shown to be kept in Table 1). But, capacity and total running cost do not count the initial moisture content. It should be the calculation of running cost of removing 1kg moisture is more accurate, as shown in Fig.15, reveals that lying type has the smallest cost performance. (2) In tent house type, the air leak and the unbalance of the position of bottom is found. The air leak makes the static pressure lower, and the fluctuation of the rice layer depth according to the unbalance of the bottom level causes the drying speed not to keep constant among points. It is thought that these matters make drying performance of tent house prototype lower than that of lying drum prototype because lying drum did not create these problems. So, after these mistakes were adjusted, it has been operating well. (3) Sunshine drying of over 27% high moisture rice could not be finished for a day. After all, it took 3 days to dry the high moisture rice sample because the second day became rainy. Thus, sunshine drying was affected by the climate so much that finishing time could not be expected and the quality did not keep constant. That was considered as a serious problem of sunshine drying. (4) Fig.8 shows the trend of the moisture reduction each sampling point. The mixing was so effective that the moisture content became lower and moisture deviation between the surface and the bottom became smaller. The moisture deviation between front position and back position did not create serious problem because final moisture deviation was down less than 1%. Table 4 shows the results of time study. It took hrs for each dryer to work. On 5 th work, lying drum and standing cylinder dryer expressed without problems, tent house dryer however must be adjusted its drying air duct, it took 0.2 hour to do. CONCLUSIONS AND SUGGESTION (1) Lying dryer prototype offerred good drying performance and mixing was easy, drying rate of 1.31%/h was possibly suitable to paddy drying. The broken rice percentage was small of 2.0%; drying cost was VND/kg. But, this created some problems e.g.: (i) Drying bin must be always full before operating start, (ii) Investment cost was more expensive than two other dryer types in the test. (2) Tent house dryer prototype offerred lower drying performance in this experiment. But, in terms of farmer practice improvement, its performance became higher. It was thought that this type can be commonly used because of (i) flexibility of the volume of input wet rice, (ii) multi use, (iii) cheapness, and (iv) easiness of taking apart; (v) low broken rice percentage (3.5%), relatively low drying rate (0.8%/h), the lowest drying cost (51.83 VND / kg). (3) Standing dryer prototype addressed a feature investment cost of cheapness: drying rate of 1.23%/h, broken rice percentage of 2.5%, drying cost of 68,96 VND / kg. Mentioning to drying rice in terms of smallholders, this type could be useful. (4) Three dryer prototypes offerred a good feature, suitable to small holders with low income. They need to be developed through training, demonstration, transferring to farmers.

12 Studying and fabricating simple small dryers REFERENCES Baker CGJ The design of flights in cascade rotary dryers, Drying Technology, p Brooker DB, W Fred Bakker-Arkema, W Carl.Hall Drying Cereal Grains, Westport, Connecticut, The AVI publishing company, Inc. Brooker DB, W Fred Bakker-Arkema, W Carl.Hall Drying and Storage of Grains. An AVi Book published by Van Nostrand Reinhold, New York Cham RR, E Highley, and G. Johnson Grain Drying In ASIA, ACIAR PROCEEDINGS, No. 71. Australian Centre for International Agricultural Research, Canberra. Champ BR, E Highley, and GJ Johnson Grain Drying in Asian, ACIAR Proceedings, N0 71. Australia Centre for Internatinal Adricultural Research, Canberra. SUMMARY IN VIETNAMESE Nghiên cứu và chế tạo máy sấy lúa phục vụ nông hộ có qui mô trang trại nhỏ Bộ môn Cơ Điện của Viện Lúa Đồng bằng Sông Cửu Long đã nghiên cứu cải tiến và chế tạo một vài mô hình mẫu của máy sấy nhỏ phục vụ cho nôn dân cho diện tích ruộng ít, ở vùng sâu. Từ 00 đến 02, máy mô hình máy sấy theo yêu cầu như vậy đã được nghiên cứu và chế tạo. Đó là lều sấy sử dụng quạt thông gió, máy sấy trục đứng, máy sấy vĩ ngang. Những công cụ này đã đáp ứng được yêu cầu của sản xuất lúa trong vụ hè thu, đặc biệt tại tỉnh Cần Thơ. Đặc điểm của chúng là máy sấy nhỏ (khả năng 1 đến 2 tấn lúa / mẽ), cấu trúc đơn giản, dễ chế tạo, đầu tư vốn thấp, giá sấy thóc rẽ, dễ vận hành, thời gian sấy nhanh và phẩm chất lúa sấy tốt (tỉ lệ gạo gãy thấp)